1. Field of the Invention
The present invention relates to membrane potentiometers, and more particularly to magnetically-activated membrane potentiometers.
2. Background and Related Art
Film/membrane potentiometers on the market operate in one of two distinct manners: The first type operates with an actuating pressure on the tapping pressure pin. Over time the actuating pressure on the tapping pressure pin strips the upper plastic film on the resistive path, causing the film to wear out. As the plastic film of the resistive path wears out, the resistive path may become increasingly pre-formed and as a result the top layer can pre-actuate electrically, or the contact wiper can physically tear the top layer. This decreases the life of the film potentiometers and can result in locations of lost contact. In addition, such film potentiometers require a parallel guidance of the tapping pressure pin. This increases manufacturing costs as relatively large additional structure must be provided to support and provide the guidance of the tapping pressure pin.
The second type utilizes a magnet either above the top surface of the film potentiometer or a magnet beneath the top layer of the film potentiometer, both of which cycle across the potentiometer, either on the film or directly on the conductive traces. This construction, while providing opportunities to use magnets to produce potentiometric feedback, remains limited to the abrasion of the magnet, which moves across the surfaces to produce the required feedback when the connecting magnet moves. Hence, wear and tear is still a concern when using magnets in or on the film potentiometer. An additional limitation of this style of magnetically-actuated potentiometer is the amount of magnetic force required to contact the wiper and the collector, which can be significant and may impact the usability of the product. Additionally, if there is a random separation of the two attracting magnets (one being either on top of the film potentiometer or inside the top layer and the second being below the resistive trace, “driving” the second magnet to motion across the film potentiometer), the top magnet could move to a different position without connecting to the driving magnet, thus losing electrical position.